same symptom, 95 240sx, m2-atx... tested w/multimeter, no symptoms on the bench either, must spike voltage or go negative... this should be in the m2 faq.

i got this dreaded problem today.

m2 works fine when i start the car, but when i go to shut it off the motherboard powers off immediately and then restarts- just like it lost power for a split second. then, after a few more seconds while its trying to reboot, the m2 sends the shutdown signal as its supposed to and it shuts down.

thing is its been working fine for weeks, and nothing that i know of has changed. these problems are getting to be such a pita... im starting to question the durability of the m2atx (already returned one of them!)

m2 was powered off acc for climate control, and while normally the truck doesnt shut off the acc while starting it DOES shut off the power if the A/C is left ON. smart setup i guess, because it fooled me. there is no doubt this could have been the reason i have had weird shutdown problems in the past... as long as the A/C is OFF when i turn off the ignition, everything is peachy.

so right now im switching things up and m2 will get power from a dedicated battery circuit. for control, the remote outputs of my 791xv remote starter will fire up a relay to switch the REM on the m2atx. this way i can remotely fire up my pc if i want to, and all other problems should be eliminated.

Without shutting of the IGN, remove the wire from the IGN leading to the M2 and see what happends...
Also, what do you mean the 'ground is to ground'? It's attached to the chassis of the car?

Ok, I started the car with the IGN wire disconnected.. With the car running I then applied the IGN wire to the M2.. It powered up correctly after 5 seconds.. I let it run for a minute or so and then removed the IGN wire from the M2..

It began the hibernation process.. While it was still in the process I turned off the car.. It didn't shut down and continued hibernating correctly..

So, it has to be something going on with the IGN wire only when the car is shut off because it works fine when I manually remove the IGN wire from the M2..